In a mobile communication system, there may be many uncertainties in a communication process because of time variant characteristics of a wireless fading channel. On one hand, in order to improve a system throughput, a high-order modulation with high transmission rate and an error correcting code with less redundancy may be adopted to perform communications. When this technology is adopted, the system throughput may be effectively improved when a Signal to Noise Ratio (SNR) of the wireless fading channel is ideal; but it may be impossible to ensure that communications are performed reliably and stably when the channel dips into a deep fade. On the other hand, in order to ensure the reliability of communications, a low-order modulation with low transmission rate and an error correcting code with more redundancy are adopted to perform communications. When this technology is adopted, it may be possible to ensure that communications are performed reliably and stably when the wireless fading channel dips into a deep fade; but when the SNR of the channel is high, because the transmission rate is low, the improvement of the system throughput may be restricted, which wastes resources. In an early stage of development of mobile communication technologies, people may try to resist the time variant characteristics of the wireless fading channel by solely improving transmitting power of a transmitter, and may use a low-order modulation and coding method with more redundancy to ensure the communication quality of a system when the channel dips into a deep fade. However, the problem regarding how to improve the system throughput is not taken into consideration. With the development of technological level, an adaptive coding and modulation technology, which belongs to a most typical link adaption technology, emerges. The adaptive coding and modulation technology may adaptively regulate, according to a channel state, a transmitting power of a channel, a modulation and coding mode and a frame length of data to overcome the time variant characteristics of channel, thereby achieving the best communication effect.
In a Long Term Evolution (LTE) system, for realizing a downlink adaptive coding and modulation technology, control signaling including CSI may be transmitted in the uplink. The CSI may include a Channel Quality Indicator (CQI), a Precoding Matrix Indicator (PMI) and a Rank Indicator (RI). The CSI may reflect a physical downlink channel state. A base station, for example, an Evolved Node B (eNodeB) may use the CSI to perform downlink scheduling and perform coding and modulation of data.
In order to acquire the CSI, the eNodeB may send a downlink Reference Signal (RS). User Equipment (UE) may acquire the CSI by performing channel and interference measurement according to the RS. In the LTE system, the RS usually used for acquiring the downlink CSI may include a Cell-specific Reference Signal (CRS) and a CSI Reference Signal (CSI-RS). The CRS is introduced in the LTE standard of Release-8 (Rel-8). Corresponding to 1/2/4 antenna port(s), the CRS for the 1/2/4 antenna port(s) is defined. The CSI-RS is introduced in the LTE standard of Release-10 (Rel-10), mainly used for a Transmission Mode (TM) 9/10. Corresponding to 1/2/4/8 antenna port(s), the CSI-RS for the 1/2/4/8 antenna port(s) is defined. For a specific antenna port configuration, the RS may occupy, on frequency-domain resources, specific Resource Elements (REs) according to a fixed distribution pattern. Both the CRS and the CSI-RS may be sent on a whole system bandwidth. After acquiring the CSI, the UE may send the CSI to the eNodeB by way of periodic feedback or non-periodic feedback.
The LTE system defines relevant CSI (CQI/PMI) feedback types. For a non-periodic CSI report, the CQI feedback types may include wide-band CQI, UE selected sub-band CQI, and higher layer configured sub-band CQI. When the wide-band CQI feedback type is configured, the UE may feed back the CSI reflecting the channel quality of the whole system bandwidth. When the UE selected sub-band CQI feedback type is configured, the UE may select M sub-bands, and may report location information of the M sub-bands and the CSI reflecting the whole channel quality of the M sub-bands. For the higher layer configured sub-band CQI feedback type, the UE may report the CSI of each sub-band. For a periodic CSI report, the CQI feedback types may include wide-band CQI and UE selected sub-band CQI. When the UE selected sub-band CQI feedback type is configured, the UE may report in one sub-frame the CSI of a sub-band of a Bandwidth Part (BP), and report information about different BPs in different sub-frames.
With the richness of application requirements and the development of wireless communication technology, future communication systems (e.g. the fifth generation (5G) communication system) may face more complex wireless channel environments. For example, a huge number of users and burst service data may bring about more interference, and a big path loss and a deep fade may reduce the SNR of received signals. Such a complex channel condition may cause an inaccurate acquisition of the CSI, and the inaccurate CSI or mutational channel may make a CSI mismatch phenomenon even worse. The CSI feedback in a related technology, mainly aiming at the CSI feedback for the whole bandwidth or sub-band, may not provide, on data frequency resources, like a Physical Downlink Shared Channel (PDSCH) in the LTE system, a timely feedback on a channel and interference condition. Moreover, in the related technology, the CSI is measured by adopting pilot frequencies such as the CRS and the CSI-RS, and the measurement accuracy of these kinds of pilot frequencies may be limited under an extremely low SNR scenario. Therefore, a new type of CSI measurement and feedback solution may be needed to improve the CSI accuracy and provide more timely and more proper feedback of the channel state on the data frequency resources, thereby realizing channel adaptation better.
An effective solution has not been presented aiming at a problem in the related technology that CSI measurement accuracy is not high and CSI feedback on a data sharing channel is not timely.